Secure garden

Jagvir Goyal

A spurt in cancer cases in North India and awareness about the ill effects of excessive use of pesticides has made people look for organic food or make effort to grow their own vegetables. While a company has launched vegetable and fruit purifier which has not been much successful, trend of growing own vegetables is fast catching up in urban areas. ‘Plant to  Plate’ is becoming a tagline for the urban elite. 

As a result everyone wants to have his own kitchen garden, grow vegetables and enjoy healthy and pesticide-free food. 

As far as one is living on  the ground floor, there is no problem in developing a kitchen garden. One can always find a corner or some space in the front or back courtyard to develop the kitchen garden. And there are no structural issues involved. The challenge lies in developing a kitchen garden while living on the first floor or higher elevations, in flats or apartments. Here, the front or back balconies are considered to be most suitable locations for developing kitchen garden because plenty of sunlight and air are available. What is more important to watch are the structural features of the kitchen garden.

Let’s have a look at the related engineering aspects of this new trend:

Structural features

Developing a kitchen garden in a balcony or on the terrace means deposition of extra earth load over the balcony or terrace slab. This extra load on the slab causes stresses in it and at the slab supports. Application of water to the plants may cause retention of water on the balcony or terrace leading to dampness in the area. Then establishment of proper drainage system has also to be taken care of. 

Thus, there are three major structural features: Structural design, water proofing and drainage arrangements.

design: The design of the floor slab over which a kitchen garden is to be developed, needs to be rechecked by taking into account the extra load of earth and other items that shall be rested over the slab. Often the weight of earth is counted but the weight of extra pots that are laid there is ignored. Weight of pots is significant and needs to be considered as ‘pointed load’. It is better to use stands for the pots instead of placing them directly on the slab to disperse their load over a wider area.To cause lesser load on the slab, wooden, plastic, aluminium or fibre pots should be selected. The weight of soil should be considered as saturated slab so that weight of water also gets counted. Normally, the thickness of soil mixed with manure layer thickness is 8 inch to 10 inch. By rechecking the design, it should be ensured that the slab and its supports can wear the extra load being put on it without causing any cracks in them.

Cantilevers: If a kitchen garden is being developed in a balcony, be extra cautious. Most of the balconies are designed as cantilevers and cantilevers are infamous for their failure in the history of civil engineering. A cantilever is simply projecting from a wall without any other support below it. If the cantilever slab is found to be unsafe for extra load being caused on it, supports below it should be provided before developing kitchen garden in the balcony. It should also be seen that making all this arrangement of extra supports below the cantilever slab is not uneconomical.

Waterproofing: Needless to say that waterproofing of kitchen garden slab is as important as its structural design. To provide waterproofing, proper treatment should be given to the slab before laying the garden. The slab surface should be cleaned well with wire brushes and then treated well by applying polymer-based flexible water proofing layers on it. While doing this, if any cracks are noted in the slab, these should be treated well by converting them into small V-shaped crevices and then filling them with a polymer modified mortar. 

For waterproofing, it is better to lay a layer of 6mm thick 1 : 3 cement sand mortar over the slab after adding waterproofing compound to the mortar. Over the mortar layer, a layer of tiles can be laid in slope as per drainage plan.

Drainage arrangement: In case of balconies and terraces, it is common practice to provide proper slope to the slab area during their construction, for drainage of rain water through rain water pipes. A concrete ‘gola’ at the junction of the slab and parapets is also provided in normal practice as these junctions are the vulnerable leakage points. 

While developing a kitchen garden in balcony or on terrace, a 2 inch thick layer of water-borne aggregate or shingle or pebbles should also be laid over the tiles in the same slope by maintaining the two-inch thickness uniformly so that the slope of tiles is acquired by the stone layer also. This whole system shall provide effective drainage arrangement. All these loads should be considered while rechecking the structural design of the slab.

Geo-membrane provision: For creating best kitchen garden arrangement, it is better to lay a thick layer of geo membrane on the tiles before covering them with the pebbles or stones. 

However, this is optional as the geo-membrane layer will causeadditional cost. Otherwise, a HDPE net layer can be laid over the stones. This geo membrane or HDPE net layer will prove helpful in holding back the soil while excess rain water in balcony gets drained off to the rain water pipes. Next, the soil layer can be laid as the base for it is now ready to receive the soil. 

The water connection: Provision of a water connection in the balcony or terrace is essential for a productive kitchen garden growing vegetables. Generally, we keep a tap on the terrace or balcony to draw water. Same tap can be used for watering the vegetable plants in kitchen garden. 

Outsourcing the job: As growing on vegetables is becoming a craze among people, many companies who undertake development of kitchen garden now exist in every city. An online search will tell you about their existence. And howsoever small space be available with you, they would develop your kitchen garden in it. Even a 4  x 4 feet space is converted by them. Contact them and assign them the job. 

However, just ensure that all structural aspects are taken care of and joy of having a kitchen garden is not marred by structural cracks or dampness or leakage or failure of balconies.

— The writer is former HoD and engineer-in-chief, civil engineering department in 

a Punjab PSU